1. Field of the Invention
The invention relates to systems or methods for cladding superalloy components, such as service-degraded turbine blades and vanes, by laser beam welding. The welding/cladding path is determined by prior, preferably real time, non-contact 3D dimensional scanning of the component and comparison of the acquired dimensional scan data with specification dimensional data for the component. A welding path for cladding the scanned component to conform its dimensions to the specification dimensional data is determined. The laser welding apparatus, preferably in cooperation with a cladding filler material distribution apparatus, executes the welding path. In some embodiments a post weld non-contact 3D dimensional scan of the welded component is performed and the post weld scan dimensional data are compared with the specification dimensional data. Preferably the welding path and/or cladding application are modified in a feedback loop with the pre- and/or post-welding 3D dimensional scanning.
2. Description of the Prior Art
“Structural” repair of gas turbine or other superalloy components is commonly recognized as replacing damaged material with matching alloy material and achieving properties, such as strength, that are close to the original manufacture component specifications (e.g., at least seventy percent ultimate tensile strength of the original specification). For example, it is preferable to perform structural repairs on turbine blades that have experienced surface cracks, so that risk of further cracking is reduced, and the blades are restored to original material structural and dimensional specifications.
Repair of nickel and cobalt based superalloy material that is used to manufacture turbine components, such as turbine blades, is challenging, due to the metallurgic properties of the finished blade material. The finished turbine blade alloys are typically strengthened during post casting heat treatments, which render them difficult to perform subsequent structural welding. When a blade constructed of such a superalloy material is welded with filler metal of the same or similar alloy, the blade is susceptible to solidification (aka liquation) cracking within and proximate to the weld, and/or strain age (aka reheat) cracking during subsequent heat treatment processes intended to restore the superalloy original strength and other material properties comparable to a new component.
One known superalloy joining and repair method that attempts to melt superalloy filler material without thermally degrading the underlying superalloy substrate is laser beam welding, also known as laser beam micro cladding. Superalloy filler material (often powdered filler) compatible with or identical to the superalloy substrate material is pre-positioned on a substrate surface prior to welding or sprayed on the surface with pressurized gas through a channel during the cladding process. A “spot” area of focused laser optical energy generated by a fixed-optic laser (i.e., other than relative translation, laser and substrate have a fixed relative orientation during laser beam application) liquefies the filler material and heats the substrate surface sufficiently to facilitate good coalescence of the filler and substrate material, that subsequently solidify as a clad deposit layer on the substrate surface. Compared to other known traditional welding processes, laser beam micro-cladding is a lower heat input process, with relatively good control over melting of the substrate and rapid solidification that reduces propensity to cause previously-described solidification cracking. Lower heat input to the superalloy substrate during laser welding/cladding also minimizes residual stresses that otherwise would be susceptible to previously described post-weld heat treatment strain age cracking. While laser cladding welds have structural advantages over traditionally-formed welds, practical manufacturing and repair realities require larger cladding surface area and/or volume coverage than can be filled by any single pass applied cladding deposit.
To meet needs for adding volume to superalloy components, a laser-cladded deposit on a substrate can be formed from single- or two-dimensional arrays of adjoining solidified clad passes. Multiple laser-welded cladding passes and layers can be applied, under automated control, to build surface dimensional volume. Creating arrays of laser-clad deposits often results in microcracks and defects in the deposited material and underlying substrate in the heat affected zone material. Some defects are related to lack of fusion (LoF) that is common when there is insufficient localized laser optical energy heat input. Often a substrate, such as a turbine blade, requires structural repair filling of a missing volume of the blade substrate material with an equivalent volume of superalloy filler, in order to restore the blade's original structural dimensions. In known laser cladding techniques the missing blade substrate volume is filled with a two-dimensional filler weld array of individually-applied laser clad deposits or passes. The laser beam focus position and substrate surface are moved relative to each other under automated control after a single deposit formation to weld the next deposit, analogous to a series of abutting, overlapping bumps or dots. With known multi-dimensional filler material depositing equipment, either a layer of the filler particles (often in powder form) are prepositioned in a layer on the substrate surface or directed through a pressurized gas-fed nozzle over the laser “spot” projected location.
Automated or semi-automated laser weld repair of superalloy turbine component substrates requires definition of each part geometry for tracking purposes, so that the laser cladding path applies solidified deposits on the component's desired surface portions. Component measured actual geometric outline information is compared with desired component specification geometric outline information. The comparison identifies component undersized surface portions in need of solidified filler. The comparison information is used to program the laser cladding or welding path, with expectation that the newly filled portions will meet or exceed the desired specification dimensions. If the newly filled portions of the welded component remain undersized the component must be remeasured and rewelded with a second welding path. After application of one or more welding paths the welded component is inspected for weld quality. Voids or cracks remaining after or created by during the welding process may render the component unsuitable for service, in which case the prior welding effort and expense was wasted. If the post welding inspection indicates that the part is serviceable any post weld excess material is removed by known metal working processes.
In known welding processes component or part outline geometric information is typically collected before repair processing by a camera and defined by contrast measurement. An optical camera, which may be in a machine vision subsystem of an automated welding system, captures a visual image of the turbine component outline. Optical contrast is used to define the component outline or footprint. The automated welding system utilizes the optically defined component outline and the component's desired dimensional specification outline to establish the welding path of relative movement between the component and welding spot (i.e. part movement on a motion control work table, or movement of the welding equipment, or both). The welding system, executing the welding path, dads the component surface to fill missing volume between the actually defined outline dimensions obtained by the optical camera system and specification dimensions.
Traditional optical methods to define repaired component geometry and outline require specialized part illumination and are lacking in resolution and precision. The optical measurement methods only generate planar two dimensional outline information, with the height dimension effectively only inferred by shadow resolution. Thus the welding path executed by the welding apparatus only approximates the two dimension outline of the component. The filler height determination is determined empirically by the welding operator or the automated welding path processor by estimating the number of successive layers needed to obtain the component specification height dimensions. Traditional optical component measurement methods can not be used during repair as feedback to adjust processing equipment in case of component part change in physical condition (e.g., thermal distortion), movement, misalignment of component surface and welding, misguided weld path, or creation of weld defects (e.g., voids and/or cracks) apparatus during repair. Besides the previously identified optical measurement system illumination, resolution and precision deficiencies they cannot obtain visual images through smoke and high-intensity ultraviolet (UV) emissions generated by the laser cladding/welding system during the welding process. Smoke scatters reflected optical camera illumination and high intensity UV emissions overpower the optical camera's ability to capture a visual image.
U.S. Pat. No. 5,504,303 proposes use of a non-contact laser profilometer to obtain 3D dimensional topography measurement information of a diamond surface. The measured information is compared to desired specification information. Subsequently an ablation laser cuts surface portions identified as being too thick compared to the desired specification. The cut surface is subsequently re-scanned with the laser profilometer to determine whether the surface now meets the desired thickness specification. Cutting and scanning are repeated sequentially until the surface conforms to the desired specification. It is further stated in the patent that the profilometer and ablation system can utilize a common laser device.
Thus, a need exists in the art for turbine component laser cladding systems or methods that in real time acquire component dimensional data, compare the acquired dimensional data with specification dimensional data and determine a welding pattern for building up the component surface in conformity with the determined welding pattern, so that the welding pattern is dynamically determined and is adjusted in response to transient changes occurring during the welding process. Examples of such transient changes include but are not limited to component thermal distortion, movement and/or misalignment of the component surface and the welding apparatus, misguided weld path, or creation of weld defects (e.g., voids and/or cracks) during the welding process.
Another need exists in the art for turbine component laser cladding systems or methods that in real time perform subsequent post weld measurement of the component surface and determining whether the post weld surface measurement data are in conformity with desired specification dimensional data and/or weld quality (e.g., lack of voids and/or microcracks in the welded surface). To meet this need, the systems or methods preferably incorporate the post weld measurement and/or inspection within a real time feedback loop to adjust the welding process dynamically, so that the welded surface is formed in conformity with desired specifications.
An additional need exists in the art for turbine component laser cladding systems or methods that in real time or sequentially acquire dimensional data, compare acquired dimensional data with specification data, determine a welding path and welding processes for building up the component surface in in conformity with the determined welding pattern, and performing the welding by transferring optical energy from the welding laser to the filler material and substrate that fuses the filler material to the substrate as a filler layer without causing thermal degradation to the substrate. To meet this need to avoid thermal degradation the systems or methods preferably vary optical energy transfer based on component surface topology.
Yet another need exists in the art for turbine component laser cladding systems or methods that acquire dimensional data in spite of smoky conditions and/or ultraviolet emissions caused during the laser welding process, whether the acquisition occurs in real time or sequentially with the laser welding process.